1. Field of the Invention
The present invention relates to a billing system on asynchronous transmission mode (ATM) switching system. More particularly, it relates to a relief method of billing data in ATM switching system when a failure occurs on switched virtual connection calls that subscribers connect or disconnect, or the system is resumed.
2. Description of the Prior Art
In a conventional system, a call data saving function has been used to relieve billing data by periodically evacuating the billing data. In the system, the fee is charged according to a calling time, and the method is different from a method in the ATM switching system.
On the other hand, a call is charged according to the number of normal cells transmitted through a connection in an ATM switching system (for example, refer to Japanese Unexamined Patent Publication No. HEI 4-12763). Then, ATM terminator counts the number of the cells in order to perform the processing at high speed. Therefore, the billing data is formed by a cell counter value read out by the ATM terminator and call control data in a call controller, which is independent of the ATM terminator.
When the billing data is relieved on initializing the device when a failure occurs (hereinafter, it is referred as to initialization), it is required to relieve bill forming data. However, the ATM switch collects the billing data formed according to the number of the cells and therefore, the reliability of the data is lacked even if the data is periodically evacuated.
This is because large amount of cells can be instantaneously transferred and even no cell can be transferred in an ATM switching service with a large capacity. If a problem of evacuating the data can be resolved, there is possibility of having much time to facilitate communications in order to collect data between the ATM terminator and the call controller, each of which is independent, and there is also the possibility of communication congestion because the amount of the access to the device becomes huge.
Because the above-described problem is recognized, only a relief method of billing data has not been provided in the existing ATM switching system.